This adds the Python files in the tests/ directory to be formatted with
./tools/codeformat.py. The basics/ subdirectory is excluded for now so we
aren't changing too much at once.
In a few places `# fmt: off`/`# fmt: on` was used where the code had
special formatting for readability or where the test was actually testing
the specific formatting.
POSIX poll should always return POLLERR and POLLHUP in revents, regardless
of whether they were requested in the input events flags.
See issues #4290 and #5172.